docs: def _explore_storage(self):
          """Generator of all files contained in media storage."""
          path = ''
          dirs = [path]
          while dirs:
              path = dirs.pop()
              subdirs, files = self.media_storage.listdir(path)
              for media_filename in files:
                  yield os.path.join(path, media_filename)
              dirs.extend([os.path.join(path, subdir) for subdir in subdirs])